I think many 'neglect' the midrange not because it's unimportant or lacking, but because it's much easier to hear issues with bass or treble (at least for me it is). If bass is too light/too intense/too muddy and treble too bright/harsh/rolled off, then the entire sound structure and tonality suffers, whereas if the mids/vocals are a touch too recessed or forward, or a little more or less organic, then it's not quite as critical as a problem in the bass or treble, and certainly won't fatigue as much as either of the other two. Of course we'd all love to mids to be dead on perfect every time, but that's a very tough trick to pull off while getting the other two right. Great bass/treble with very good mids is > than great mids with just average bass/treble. Just my 0.02.
Edit: I should add that the type of music you listen to has a huge bearing in the above assertion. If you mainly listen to vocals, then vocal purity/timbre has to be excellent, regardless of bass/treble (though bass and treble affect vocals in different ways). Whereas if most of your library is instrumental music, then as long as the mids are good and not too wonky, you'll notice it far less.